A1c of 5.7: What Prediabetes Means and the Optimal A1c Range
An A1c of 5.7% is the lowest number in the prediabetes range (5.7–6.4%). It means your average blood sugar over the last 2–3 months has crept up. It is not diabetes, and it is often reversible, especially when caught early and paired with fasting insulin.
By the LabClarity editorial team · Sources cited below
Standard vs. functional optimal ranges
| Marker | Standard range (ADA / CDC) | Functional / optimal range often used | Notes |
|---|---|---|---|
| Hemoglobin A1c | under 5.7% normal; 5.7–6.4% prediabetes; 6.5%+ diabetes | about 4.6–5.2% (LabClarity) | Reflects average glucose over about 2–3 months |
| Fasting glucose | 70–99 mg/dL normal; 100–125 prediabetes | about 75–90 mg/dL | A single morning snapshot |
| Fasting insulin | about 2–25 uIU/mL | under about 5–7 uIU/mL | Often rises years before A1c |
| HOMA-IR | not usually reported | under about 1.0–1.5 | (glucose x insulin) / 405 |
| Triglyceride : HDL ratio | not usually reported | under 1.5 (ideally under 1.0) | Simple insulin-resistance clue |
Ranges are typical U.S. values for adults and differ between laboratories. Functional ranges are interpretive targets used by some clinicians, not diagnostic criteria.
What A1c measures
Hemoglobin A1c is the percentage of hemoglobin in your red blood cells that has sugar stuck to it. Because red blood cells live about three months, A1c gives a rolling average of blood sugar. An A1c of 5.7% corresponds to an estimated average glucose of about 117 mg/dL. The CDC and American Diabetes Association define 5.7–6.4% as prediabetes and 6.5% or higher, confirmed on repeat testing, as diabetes. The CDC estimates that more than 1 in 3 U.S. adults has prediabetes, and most don't know it.
Standard vs optimal: why 5.7% is late, not early
Blood sugar is one of the last things to change in insulin resistance. For years the pancreas can compensate by making more insulin, keeping glucose and A1c "normal" while fasting insulin climbs. By the time A1c reaches 5.7%, that compensation is often starting to slip. That's why functional clinicians look for an A1c closer to about 5.0–5.2% and pair it with fasting insulin. Our HOMA-IR calculator guide shows how to spot insulin resistance before A1c moves.
Can an A1c of 5.7 be reversed?
Often, yes. In the landmark NIH-funded Diabetes Prevention Program, people with prediabetes who lost about 7% of body weight and did 150 minutes a week of activity cut their risk of developing type 2 diabetes by 58%, and by 71% in those over 60. A 2024 meta-analysis of 44 trials found that lifestyle weight loss programs increased the chance of returning to normal blood sugar, with benefits growing as weight loss increased. Practical levers include:
- Resistance training and a 10–15 minute walk after meals, which lower post-meal glucose.
- Prioritizing protein and fiber and cutting sugary drinks and refined carbohydrates.
- Sleep: even a few nights of short sleep reduce insulin sensitivity.
- Discussing medication (for example metformin) with a clinician when risk is higher.
When A1c can mislead
A1c depends on red blood cell lifespan, so anything that changes it skews the number. Iron deficiency and B12 or folate deficiency (cells living longer) can push A1c falsely higher, while recent blood loss, hemolysis, kidney disease, pregnancy, or some hemoglobin variants can make it falsely lower. If your A1c doesn't match your fasting glucose, ask about a fructosamine test, an oral glucose tolerance test, or a few weeks on a continuous glucose monitor. Check your ferritin and B12 as well.
Why prediabetes matters beyond diabetes
Even without progressing to diabetes, prediabetes is linked with higher cardiovascular and kidney risk. Insulin resistance tends to raise triglycerides and ApoB particle number and lower HDL, so look at your ApoB and lipid panel and hs-CRP together with A1c.
Questions to ask your doctor
- Can we confirm this with a repeat A1c and a fasting glucose, and add fasting insulin?
- Could anemia, low iron, or low B12 be affecting my A1c result?
- Would an oral glucose tolerance test or a short trial of a continuous glucose monitor help?
- Am I a candidate for a National Diabetes Prevention Program class, or for medication?
- How often should we retest, and what A1c should I aim for?
Have your own Labcorp or Quest numbers?
Enter your results into the free LabClarity decoder to compare each marker against standard and functional optimal ranges, calculate HOMA-IR and TG:HDL, and spot root-cause patterns. Want the complete picture? The full Detective Report ($19) adds every pattern, a prioritized follow-up test list, and a printable summary to bring to your doctor.
Helpful tools (affiliate links)
- At-home A1c test kits [affiliate link] — Useful for checking progress between lab draws.
- Blood glucose meter kits (for post-meal checks) [affiliate link] — Testing 1–2 hours after meals shows which foods spike you.
As an Amazon Associate, LabClarity earns from qualifying purchases at no extra cost to you. Talk to your clinician before starting any supplement.
Frequently asked questions
Is an A1c of 5.7 bad?
An A1c of 5.7% is the lowest value in the prediabetes range (5.7–6.4%). It is an early warning, not a diabetes diagnosis, and it is often reversible with changes to activity, diet, weight, and sleep.
What is an optimal A1c level?
Standard guidelines call anything below 5.7% normal. Many functional clinicians prefer about 4.6–5.2%, ideally alongside a low fasting insulin, because blood sugar often rises late in insulin resistance.
Can prediabetes be reversed?
Often, yes. In the NIH Diabetes Prevention Program, modest weight loss of about 7% and 150 minutes a week of activity reduced progression to type 2 diabetes by 58%. Many people return to normal blood sugar levels.
Can low iron raise A1c?
Yes. Iron deficiency and some B12 or folate deficiencies can make A1c read falsely high because they change red blood cell turnover. If A1c and fasting glucose don't match, ask your clinician about other tests.
Related LabClarity guides
Sources and further reading
- CDC — A1C Test for Diabetes and Prediabetes
- NIH NIDDK — Recommended Tests for Identifying Prediabetes
- NIH NIDDK — Diabetes Prevention Program (DPP)
- American Journal of Clinical Nutrition (2024) — Lifestyle weight loss interventions and regression to normoglycemia in prediabetes
- Mayo Clinic — Prediabetes: Symptoms and Causes